The present invention generally relates to an improved ground protection device combining specially designed reactive/resistive filtering components placed in such a way to work in unison with protective safety elements as sophisticated as longitudinal transformers, sense electronics, rectifiers, and trip coils or as simple as thermal-magnetic trip circuitry in order to disconnect power in the case of a fault condition hazardous to humans, thereby providing a fully integrated device that stabilizes the ground reference plane for electronic system protection along with circuitry to control power flow during fault conditions.
“Conventional” grounding techniques utilize different methods in an effort to improve the integrity of the digital ground reference, including running cross sections of braided copper wire in 1 ft×1 ft sections to attempt to provide equi-potential grounding to reduce or eliminate undesirable electrical “noise.” Various forms of ground control have been tried over the years in different applications, although most techniques still rely on methods that either intentionally float the ground or add secondary ground reference points between equipment, which can under certain circumstances create a hazardous ground potential difference.
A word about grounding and other forms of protection: Most surge suppressors/surge protection devices (SPDs) and Electromagnetic Interference (EMI) filters do require grounding and use the grounding reference to block, absorb, or shunt impulses originating on the hot or neutral. While it is still considered good practice to use protective elements in all three modes (Line to Neutral, Line to Ground, and Neutral to Ground) many devices now only utilize suppressive elements between Line and Neutral so as to not contribute to interference on the ground line.
U.S. Pat. No. 5,689,180 is an example of an isolated electrical power supply based upon transformer technology.
U.S. Pat. No. 5,666,255 (“the '255 patent”) discloses transformer-less conditioning of a power distribution system consisting of an electronically enhanced filter (EEF), a ground fault circuit interrupter with a connection to ground, and “low” and “high” level ground conditioning. There are however some important limitations to the '255 patent. First, although the '255 patent discloses a connection to ground through a mid-point tap with capacitors between line to ground and neutral to ground (and/or) via the ground fault circuit interrupter (GFCI), it also states, at Column 2, line 64, that “[t]he power distribution system has a connection to ground and may have a ground line.” The '255 patent specifically cites, at column 3, line 5, that “[t]he common mode filter has an impulse capacitor connected at one end to the midpoint tap and at the other end to ground. The common-mode filter utilizes the inductors of the power and neutral lines [and] an impulse detector and switch . . . adapted to close upon detection of the transient impulse at the mid-point tap so as to attenuate the transient impulse by shunting it to ground.” In addition, the power conditioner disclosed in FIG. 9 and column 10, line 51, “provides another type of normal mode and common mode filter for operating on hi-polar impulses with zero or small values of operating voltage” for communication systems. And at column 11, line 32, the power conditioner is described as meeting “the attenuation specification when tap 72 [the neutral-to-ground tie to the EEF] has an operating voltage nearly equal to zero volts . . . ” Most important, as described in the '255 patent at column 11, line 48, “[g]round conditioning can be defined as the safe insertion of an impedance in the ground line 40 in the electrical circuit of the power distribution system without compromising electrical fault protection.” However, the '255 patent specifically discloses, at column 11, line 56, that “[t]ypically, ground references are described as earth ground and safety ground. Earth ground (EG) is a ground reference with line that returns to earth potential (absolute ground) with as little impedance as practical. Safety ground (SG) is a near earth potential, low impedance reference line that returns equipment ground fault currents to the over current protector.” FIGS. 10 & 11, described in this section of the '255 patent, show the distinction between low and high level ground conditioning.
U.S. Pat. No. 5,781,386 shows a ground conditioning circuit that limits the impedance capabilities for real world use. The circuit clearly has an impedance before the chassis ground connection, that is, between Earth Ground “EG” and Safety Ground “SG”. In addition, the GFCI with bypass circuit places the ground conditioning device before the GFCI and before the chassis ground connection.
U.S. Pat. Nos. 6,166,458 and 6,358,029 rely on various forms of grounding impedances or attenuation circuits in the ground in an effort to block noise, surges, ground loops and high frequency interference from degrading or destroying connected equipment. In fact, U.S. Pat. No. 6,385,029 is similar to the '255 patent in that it shares high and low level ground noise attenuation, and utilizes a capacitor (Pat '029, column 3, line 53) connected to a source and neutral lead, further connected to the primary earth ground at node A, which is electrically different from the electrical load ground line 148, which is in turn connected to a node B which is joined to a floating ground FG via lead line 150. In this respect the '255 patent and the '029 are “electrically similar” in that they distinguish an electrical difference between the earth ground input (EG in both) and the load ground (Safety G in the '255 and Floating Ground FG in the '029) which create a ground differential.
U.S. Pat. No. 6,040,969 discloses a means to meet UL leakage requirements while providing “superior” suppression of neutral-to-ground voltage and disturbances, in addition to correcting reverse polarity conditions as detected by the sensing circuit described in the second embodiment of the of the '969 patent. In actuality, the only performance advantage achieved by the '969 patent is that its polarity protection circuitry enables it to reduce the rating of the surge protection components between neutral and ground, and if certain conditions exist, a direct short is created instead of the standard surge protection circuitry.
U.S. Pat. No. 6,697,238 discloses a GFCI with secondary test switch contacts which senses improper wiring of the GFCI device causing the secondary circuits to short circuit between the AC input terminals, blowing a fuse to disable the GFCI, but does nothing more to protect against ground referenced noise and neutral to ground potential differences.
U.S. Pat. No. 6,560,079 applies to a thyristor whose gate is controlled by the potential state of the ground conductor; if this state is substantially at zero, the gate closes to allow flow of current to load; if this state is not at substantially zero volts with respect to ground, the gate opens, turning off power to the loads. The drawback here is that the ground typically carries substantially more than zero volts, so depending on the sensitivity threshold, false tripping could occur.
In general, there is a misunderstanding regarding typical GFCIs. Conventional wisdom would lead one to believe that these devices actually require a connection to the ground line to sense a ground fault condition and block power. To the contrary, standard ground fault interrupters do NOT require any connection to the ground line. Standard GFCIs have a number of inherent drawbacks, which can lead to premature failure, false tripping, internal circuit damage, external load damage, and most importantly, a false sense of security in terms of safety.
Effective grounding serves many purposes, including provision of the power system reference, personnel protection from electrical shock, lightning protection, digital logic reference, equalization of ground potentials to inhibit ground loops and current from flowing through data and audio/video cabling. Conventional conditioning technologies, power filtering devices, surge suppressors (SPDs), EMI filters, and ground fault circuit interrupters perform many important functions; however, they still tend to fall short when it comes to real ground line problems.
There have been a number of methods developed over the years to address unwanted frequencies in order to protect operation of digital circuitry. However, each device has its own drawbacks, or is just too costly to implement, making the design itself not an option in the market especially if it is too costly or unable to meet safety standards. In addition, “home-grown” solutions to interference problems have been developed ranging from forming a coil in the power cord (which could actually create additional impedance to 60 cycle fault current and high frequency interference), to floating the ground wire by lifting the ground pin, to using driven ground rods at more than one point within a facility to attempt to achieve a zero-reference earth ground, to implementing balanced power systems where 60 volts is connected between line and ground and 60 volts between neutral and ground. Each of these situations can create additional safety and performance problems for the user and the equipment, so none of these “fixes” really address the full extent of the electrical and electronic problems.
Two issues are important to understand as they relate to the purpose and need for the invention disclosed herein.
First, electronic loads with sophisticated digital circuitry have taken the place of conventional electrical loads. As this digital revolution continues and technology keeps progressing at an alarming rate, the cost of new technology is driven lower and lower, while at the same time, consumers are seeking more product feature for the same amount of money with each new release/upgrade. This evolution benefits the consumer over the manufacturer, as profit margins wither away. In order to meet the higher level expectations of features versus cost, many manufacturers have eliminated excess components in their equipment to meet the market's price expectations, while still maintaining certain levels of performance.
Second, as the digital revolution evolves, the dividing lines between industries, markets and applications start to disappear. Five years ago, information technology systems (IT) and data centers were considered the “mission critical” places where line conditioners were applied. Today, digital imaging and audio/video communications have become a sub-set of every market: entertainment, gaming, home theater, banking, retail, manufacturing and control, transportation, failure analysis, security, personal and global communications. As these trends continue, the problems once only known to A/V technicians, facility engineers and electronic engineers have become common-place, even to home entertainment enthusiasts.
The problem that exists is that “fixes” implemented in professional installations cannot be used in many environments where personnel or equipment safety may be compromised (floating grounds, separate driven ground rods, balanced power, etc.). In addition, the market cannot bear the use of bulky, expensive systems relied on in the past to protect sensitive electronics, whether installed internal or external to the electronics in question.
More and more systems now rely on the conversion of signals with extremely fast transfer times having a lower and lower tolerance range for the digital signal conversion (audio, video, and digital).
Impulses are not the only occurrences that destroy chips; low and high level voltage surges, as well as very low level current flow, disrupt system performance and signal integrity. Other technologies fail to address the lower level, low currents that can more of a problem than transient impulses. Secondly, prior art does not take into consideration a two wire environment, such as DC applications.
In the audio world, the audio bandwidth is typically considered to be in the 20 Hz to 20 Khz frequency range—those that humans can actually hear. However, a much wider frequency range, from subsonic (too low to hear at 0-20 Hz) to ultrasonic levels, can and do interfere with the intended signals. Audio is affected by undesirable noise when it creeps into the intended signal, robbing the output of its dynamic range and can even burn out coils in speakers and sub-woofers. Low order harmonics 60-120 Hz can show up as what is commonly referred to as 60-cycle hum. Fixed frequency noise is any unwanted signal that remains steady (or close to it) over time such as DC offset, hum and buzz from ground loop currents, and acoustical noise from mechanical and linear loads. AC hum is the classic fixed frequency contaminant, but the harmonics (multiples of the 60 cycle fundamental frequency) are often more of a problem that couples into the signal paths relatively easily via inductive and capacitive coupling. In connection with audio and video signals, ground currents and noise create horizontal hum bars (light or dark lines that creep up on a monitor) and a low level audio hum. Impulse noises are those pops and clicks that remain on recordings, or show up in digital imaging as timing errors, jitter, or strange bits on the screen. Digital clipping occurs when a signal peak (entering through the digital reference plane) exceeds the binary range of the A/D converter or internal signal processing system.
As clock frequencies extend beyond a few hundred megahertz, digital pulse width edges into the sub-nanosecond range, and networking interfaces deliver data at rates exceeding 100 Megabits per second, the importance of a high quality power and reference ground source free of interference is essential to combat signal and data loss and improve performance. Most importantly, fast changing pulses of current and noise on the ground reference plane can cause “etching” on the integrated circuits within sensitive devices, leading to early failure of the system and corrupt data. As users invest more in high end imaging systems for uses including medical, security, entertainment, industrial, and transportation applications, they insist on the highest quality image, information output and total overall reliability on their investment.